Revealing mistake: In the scene where Doc Brown is following Biff into the tunnel, as Marty starts to pass between the cars on his hoverboard, one of the wheels on the rig supporting the hovering DeLorean is visible. (01:30:30)
Back to the Future Part II (1989)
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Directed by: Robert Zemeckis
Starring: Christopher Lloyd, Michael J. Fox, Lea Thompson, Thomas F. Wilson, Elizabeth Shue
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More mistakes in Back to the Future Part II
Biff: Go ahead, kid. Jump. A suicide will be nice and neat.
Marty: What if I don't?
Biff: [raising gun] Lead poisoning.
Marty: What about the police, Biff? They're gonna match up the bullet with that gun.
Biff: Kid, I own the police. Besides, they couldn't match up the bullet that killed your old man.
Marty: You son of a...
[Biff pulls back on the gun's hammer.]
Biff: Suppose it's poetic justice. Two McFlys with the same gun.
Trivia: When Doc and Marty arrive back in 1955 to stop the handover of the Almanac, there are 4 versions of the time machine in the area at that time - the one they just arrived in from the alternate 1985, the one Marty arrived in from the original 1985 in the first film, the one Biff arrived in from 2015 in the second film, and the one Doc buried in 1885 in the third film.
Answer: He is attempting to play the song "The Power Of Love" by Huey Lewis and The News. He was first seen playing it very well in the first Back To The Future movie when he was trying out for the school dance. Jennifer recognizes the song and is shocked that Marty who was so good at guitar was suddenly able to hardly play it.